The incident happened this morning at the ICL Boulby mine, three miles north of Staithes, which is famed for its potash, an important ingredient in producing fertilisers.
An investigation is under way into what caused the fire in the early hours of Wednesday.
A spokesman said emergency services and the mine’s rescue team tackled the fire.
“The fire has now been extinguished and all workers in the mine at the time of the incident were located and brought to the surface,” he said.
“Seven workers affected by smoke have been taken to hospital for checks.
“HM Inspectorate of Mines are at the mine and the company will be working with them in carrying out a full investigation into the incident.
“Mining operations have been suspended today.”
Last year the company announced job losses in a “significant restructuring” of its operations, including moving from producing potash to Polysulphate fertiliser.
It is 1,400m deep and its tunnels go far out under the North Sea.